This Application is a continuation-in-part Ser. No. 10/086,343 of the Application entitled xe2x80x9cUse of Aortic Pulse Pressure and Flow in Bedside Hemodynamic Managementxe2x80x9d, filed Mar. 1, 2002.
This invention relates to a treatment algorithm for managing hemodynamically unstable patients. Specifically, measurements of arterial pressure and stroke volume can be used to calculate pulse pressure variation, stroke volume variation, mean arterial pressure, elastance and cardiac power, the values of which guide treatment decisions.
The goal of cardiovascular therapy is to ensure that blood flow and oxygen delivery to the tissues is adequate to meet the metabolic demands of the tissues without inducing cardiorespiratory complications. Cardiovascular insufficiency is often referred to a circulatory shock, and is the primary manifestation of critical illness. In most clinical conditions associated with circulatory shock, the primary concerns and therapeutic options relate to three functional questions: 1) Will blood flow to the body increase if the patient""s intravascular volume is increased, and if so, by how much is the cardiovasculature pre-load responsive? 2) Is any decrease in arterial pressure due to loss of vascular tone or due to inadequate blood flow? and 3) Is the heart capable of maintaining an effective blood flow with an acceptable perfusion pressure without going into failure?
Thus, in the assessment and management of critically ill patients, the immediate questions asked by doctors are functional and physiological in their language but practical and concrete in their application. Previously, highly invasive hemodynamic monitoring was needed to define the specific hemodynamic profiles seen in circulatory shock. Application of arterial elastance analysis was limited due to the difficulty of measuring beat-to-beat stroke volume at the bedside. Prior to the advent of esophageal pulsed Doppler and robust arterial pulse contour techniques, measurement of stroke volume on a beat-to-beat basis was not possible, and clinicians did not use this analysis as part of their diagnostic algorithms. Current diagnostic and treatment protocols do not directly address the questions asked above, even though the treatment of hemodynamically unstable patients can be resolved by answering these three questions.
For example, U.S. Pat. No. 5,551,435 discloses a method of obtaining a pre-selected combination of mean arterial pressure (MAP), stroke index (SI) and cardiac index (CI) in a patient. After MAP and SI are determined, the patient""s deviation from ideal calculated values of MAP and SI can be determined, and administration of drugs and/or volume expanders is carried out to permit the patient""s MAP and SI values to reach the desired ideal combination.
U.S. Pat. No. 5,584,298 discloses a non-invasive method for calculating actual stroke volume and cardiac output using computerized algorithms. Input data includes heart rate, blood pressure, sex, age, weight and height of the patient. Based on the input data, using the algorithm, actual cardiac stroke volume of the subject is calculated and displayed as output.
U.S. Pat. No. 5,865,758 discloses an algorithm that calculates stroke volume and cardiac output using a blood pressure pulse wave obtained from the subject, measured by means of an optical sensor clipped to the ear lobe of the patient. This patent does not teach or suggest using calculated values for variables such as PPV, etc. to provide a treatment algorithm as in the present invention.
U.S. Pat. No. 6,280,390 discloses a non-invasive method for measuring blood pressure by measuring blood volume in a blood vessel with infrared detectors.
None of the above methods use pulse pressure variation and stroke volume variation to guide selection of the appropriate treatment for a hemodynamically unstable patient, in need of immediate therapy.
The present invention provides a means of optimizing treatment of hemodynamically unstable patients, based on measurements of arterial pressure and stroke volume in a patient. Stroke volume variation, pulse pressure variation, mean arterial pressure, elastance and cardiac power can be calculated based on these measurements, and used to determine the optimal treatment for patients meeting certain criteria and classified as hemodynamically unstable.
In a further embodiment, the algorithm is implemented on a computer system. Any combination of hardware and software can be used to implement the algorithm, so long as the system includes apparatus for collecting both kinds of measurements (arterial pressure and stroke volume), a microprocessor apparatus for storing measurements and the software program containing the algorithm, and for calculating stroke volume variation, pulse pressure variation, mean arterial pressure, elastance and cardiac power, and a display apparatus for viewing the results.
Based on the measurements and the calculated variables, various treatment directives are provided to the physician. Such treatment directives comprise administering an intravascular fluid infusion, an inotropic drug, or a vasoactive drug.
It is an object of the present invention, therefore, to provide a treatment algorithm for managing hemodynamic instability based on measurements of arterial pulse pressure and stroke volume.
It is a further object of the invention to provide a treatment algorithm in which calculated values for pulse pressure variation (PPV), stroke volume variation (SVV), mean arterial pressure, elastance and cardiac power are used to guide selection of a treatment for a hemodynamically unstable patient.
It is an additional object of the invention to provide a computer system to implement the treatment system and provide treatment directives to the clinician.
These and other objects will become more readily apparent from the following figures, detailed description, examples and appended claims.